1. Field of the Invention
The present invention relates to a nuclear reactor plant.
2. Prior Art
A gas such as helium can be considered as a coolant in a direct cycle nuclear reactor wherein a turbine is directly driven by the coolant heated in the nuclear reactor. However, the nuclear reactor can hardly be operated by helium because helium is inferior in cooling capability. Therefor, power density of the nuclear reactor can not help reducing. Accordingly, a core volume is required to be expanded to gain a large amount of power generative output. Consequently, a problem had been arisen such that the production cost is increased in response to an increase of the amount of materials for the nuclear reactor plant.
Carbon dioxide can be considered as a gaseous coolant in the direct cycle nuclear reactor instead of helium. Because carbon dioxide of super critical state has a couple of times as much cooling capability (heat transmission ratio and heat transportation power) as gaseous helium, etc., have. Thus, this allows the nuclear reactor to be operated in higher temperature compared with the case when helium is used as the coolant even though carbon dioxide is not condensed. Consequently, the nuclear reactor can be miniaturized.
Moreover, both temperature and pressure of a critical point of carbon dioxide (approximately 304K and 7.4 MPa) are higher than that of helium (approximately 5.2K and 0.2 MPa).
However, the coolant (carbon dioxide) is discharged from the turbine after said turbine is driven, and the coolant is compressed to around the critical point (the area out of ideal gas characteristic) in the direct cycle nuclear reactor wherein carbon dioxide is used as the coolant. Thus a compressive work can be drastically reduced compared with the case when helium is used as the coolant.
Accordingly, when a direct cycle nuclear reactor is constituted by using gaseous carbon dioxide as the coolant, output density of the nuclear reactor can be improved compared with the case when helium is used as the coolant. Consequently, this causes the nuclear reactor plant to be miniaturized for reducing construction cost.
However, even though carbon dioxide is used as the coolant in the direct cycle nuclear reactor (hereinafter is referred to as xe2x80x9cnon-condensation cycle reactorxe2x80x9d) such that the coolant is circulated under the gaseous state, the temperature of coolant at inlet of the turbine must be high temperature (approximately 700 Cxc2x0) to gain high cycle efficiency since working volume is so large to compress the gaseous coolant. Consequently, both system and equipment are greatly heated for causing a problem such as being restricted to the selection of materials for the nuclear reactor.
In order to solve the above problem, the inventors suggested a direct cycle fast reactor using Rankine cycle utilized condensation ability of carbon dioxide (Patent Application No.2000-148151).
The direct cycle fast reactor disclosed in the Patent Application No.2000-148151 will be now described with reference to the accompanying drawing of FIG. 5.
The direct cycle fast reactor shown in FIG. 5 has a nuclear reactor 111, a turbine 112, and a power generator 113. Furthermore, a regenerative heat exchanger 114, a condenser 115, and a pump 116 are provided between outlet of the turbine 112 and inlet of the nuclear reactor 111.
Besides, arrows in the figure indicate current directions of the coolant in the direct cycle fast reactor.
The coolant (carbon dioxide) in a super critical state is heated in the core of the nuclear reactor 111 for being directly introduced to the turbine 112. And then the turbine 112 is driven for driving the power generator 113, which is connected with the turbine 112. The coolant discharged from the turbine 112 becomes gaseous state to be introduced into the condenser 115 via the regenerative heat exchanger 114.
The condenser 115 has cooling water, etc., introduced from outside for allowing the coolant to be chilled. Consequently, full amount of the coolant is liquefied.
The liquefied coolant is transferred to the regenerative heat exchanger 114 by the pump 116 for being pressurized to be more than a critical pressure through heat exchanging with said coolant discharged from the turbine 112 to be increased to the temperature at inlet of the nuclear reactor 111. The coolant being increased to the supper critical state in this manner is transferred to the core of the nuclear reactor 111 to be reheated.
An electric power is generated by continuous driving of the power generator through repeating above process.
Carbon dioxide as the coolant of the condenser 115 is fully condensed in the direct cycle fast reactor of the Patent Application 2000-148151.
Certainly the coolant is liquefied in the direct cycle fast reactor. Compression for gaseous coolant performed in a non-condensation cycle reactor can be replaced with compression for a liquid coolant having a small specific volume. Therefore, a compressive work of the coolant can be reduced.
Besides, a direct cycle nuclear reactor described in the Patent Publication No.2000-148151 such as liquefying full amount of the coolant is sometimes called xe2x80x9ca full condensation cycle reactorxe2x80x9d. However, when the full condensation cycle reactor can not sufficiently chill the coolant to be less than a critical temperature [approximately 304K (31xc2x0 C.)] in the condenser 115, a pressure evacuation from the turbine 112 is increased since a saturated vapor pressure is increased. Accordingly, since the coolant can not be sufficiently expanded in the turbine 112 and a work volume to drive the turbine 112 is reduced, a heat evacuation discharged from the condenser 115 is relatively increased. Consequently, new problem will be arisen such that a cycle efficiency is not improved so much.
The present invention has been made with the forgoing background in mind. The present invention is to provide the direct cycle nuclear reactor wherein carbon dioxide is used as the coolant, and the coolant directly rotates the turbine for generating the electric power. Also the nuclear reactor of the present invention is characterized in that the heat evacuation caused by liquefying the coolant can be reduced while the compressive work can be reduced by using condensation ability of carbon dioxide. Accordingly, the subject of the present invention is to provide the nuclear reactor plant enhancing the cycle efficiency than ever by taking above mentioned characteristic.
The present invention is comprised as follows to solve the aforementioned subject.
The present invention according to the following claim 1 is a nuclear reactor plant having a nuclear reactor and a turbine, and is characterized in that a coolant in a super critical state is heated by the heat of the nuclear reactor, said heated coolant directly drives the turbine, and a gaseous coolant discharged from said turbine is chilled and compressed for being in a critical state after said turbine is driven, and then the coolant is circulated again into said nuclear reactor, and is also characterized in that carbon dioxide is used as said coolant, and a predetermined ratio of the gaseous coolant discharged from said turbine is liquefied for being compressed in a liquid state, while a rest of gaseous coolant is compressed in a gaseous state.
As described in prior art, a full condensation cycle reactor can reduce a compressive work of the coolant since carbon dioxide using as the coolant is fully condensed for liquefying. However, if the coolant can not be sufficiently low temperature, a heat evacuation (hereinafter is referred to as xe2x80x9cheat evacuation from acondenserxe2x80x9d) wastefully discharged from a condenser is increased for degrading a cycle efficiency of a nuclear reactor plant.
Therefore, the present invention relates to the nuclear reactor such that a compressive work of the coolant can be reduced to solve disadvantage of a non-condensation cycle reactor while a heat evacuation form a condenser can be reduced to solve disadvantage of the full condensation cycle reactor by compressing a part of coolant in gaseous state as well as rest of coolant in a liquid state.
Consequently, the cycle efficiency of the nuclear reactor plant could be more improved than that of both the non-condensation cycle reactor and the full condensation cycle reactor.
Besides, a ratio of being liquefied in the coolant discharged from the turbine is sometimes called xe2x80x9ca condensation ratioxe2x80x9d
The present invention according to the following claim 2 is the nuclear reactor plant as set forth in the following claim 1, comprising a first regenerative heat exchanger (hereinafter is referred to as the regenerative heat exchanger I), a second regenerative heat exchanger (hereinafter is referred to as the regenerative heat exchanger II), a first compressor (hereinafter is referred to as the compressor I), a second compressor (hereinafter is referred to as the compressor II), the condenser and a pump provided between outlet side of said turbine and inlet side of said nuclear reactor, and wherein full amount of the coolant in gaseous state discharged from said turbine is chilled by passing through the regenerative heat exchanger I and the regenerative heat exchanger II for being compressed by the compressor I, and then said full amount of the coolant is divided into said predetermined ratio of the coolant and said rest part of the coolant, said predetermined ratio of the coolant is introduced into said condenser for being liquefied and then is compressed to be more than a critical pressure by the pump and kept in a super critical state to be introduced into said regenerative heat exchanger II, while said rest part of the coolant is introduced into the compressor II for being compressed to be more than a critical pressure in gaseous state and kept in a super critical state, and then said predetermined ratio of the coolant and said rest part of the coolant are mixed with each other for being introduced into said nuclear reactor via said regenerative heat exchanger I.
The present invention according to the following claim 3 is the nuclear reactor plant as set forth in claim 1 or 2 characterized in that a fast reactor is applied as said nuclear reactor.
The present invention according to the following claim 4 is the nuclear reactor plant as set forth in claim 1 or 2 characterized in that a thermal reactor is applied as said nuclear reactor.
When the nuclear reactor plant with regard to the present invention is applied to the thermal reactor, a cycle efficiency (approximately 45%) can be gained under the condition that temperature of the coolant at outlet of the nuclear reactor is not so high (approximately 650xc2x0 C.). Said cycle efficiency is the same as it is the case when the temperature at outlet of the coolant is 900xc2x0 C. in a gas reactor of high temperature (PBMR) which is a direct cycle nuclear reactor using helium as the coolant.
When carbon dioxide is used as the coolant, carbon dioxide gas expanded in a gas turbine can be compressed in around a critical temperature. In addition, when the nuclear reactor is a partial condensation cycle reactor, the coolant (carbon dioxide) can be pressurized under the condensed liquid state until the coolant is returned to a core. Consequently, a cycle efficiency, such as it is higher than that of a direct cycle reactor of conventional helium gas turbine, can be gained.
Similarly, when the nuclear reactor plant according to the present invention is applied to a fast reactor, the cycle efficiency (approximately 40%) can be gained under the condition that outlet temperature of the coolant in the nuclear reactor is the same as that of a conventional sodium cooling fast reactor (approximately 530xc2x0 C.)
When the present invention is applied to these ones, higher efficiency can be gained than that of a conventional thermal reactor or the fast reactor. Further, the same efficiency can be gained as that of the conventional reactor even in lower temperature.